In recent years, the information processing quantity of personal computers and the information processing speed of the personal computers have been required to be increased in light of the spread of the Internet and the like. Following this, it has been becoming necessary that hard disk drives (HDDs) integrated into personal computers are also improved in capacity and information transmission speed.
In order to attain an increase in the capacity of HDDs (i.e., a density growth thereof), it is effective to make the size of magnetic particles small in recording media. However, if the size of the magnetic particles is too small, the magnetization of the individual magnetic particles is thermally unstable. Thus, recorded information is not easily kept over a long term for the following reason: if the size of the magnetic particles becomes small, the anisotropic magnetic energy KuV of each of the particles (Ku represents the anisotropic magnetic energy of the particle per unit volume, and V represents the volume of the magnetic particle) becomes small so that magnetization is oriented at random by thermal fluctuation kT (k represents the Boltzmann constant, and T represents the absolute temperature of the particle), thus, the magnetization is decreased. The limit that this is caused is referred to as the limit of superparamagnetism.
In order to extend the limit of superparamagnetism, it is effective to use magnetic particles large in coercive force. However, when magnetic particles large in coercive force are used, the intensity of a reversing magnetic field necessary for reversing the polarity of the magnetization is large so that information is not easily recorded in a recording medium. To solve this problem, heat assisting recording is known (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2009-301597, JP-A No. 2010-40112, JP-A No. 2008-159159, JP-A No. 2008-059695, JP-A No. 2008-130165, JP-A No. 2008-059645, and JP-A No. 2010-146655, and “Development of Heat-Assisting Mode Recording Head Basic Technique that Makes 5 Times Higher in HDD Capacity than Present Products and Contributes to Decrease in Consumption Power of Data Center”, Hitac, the June (2010) issue thereof, Hitachi Ltd., pp. 17-18). In heat assisting recording, a recording medium is heated just before information is recorded in the recording medium, thereby attaining the recording while the coercive force of the magnetic particles is temporarily lowered. Thus, the assisting recording has an advantage that even when magnetic particles large in coercive force are used, information is easily recorded in a recording medium.